In the measurement art it is known to use a single meter for performing any one of a number of different measurement functions. Such meters are known as multimeters, and encompass volt-ohm meters (VOM) and vacuum-tube voltmeters (VTVM) as illustrative examples. Multimeters which are digitally controlled, or have digital output displays, are known as digital multimeters (DMM). DMM's, similarly to other multimeters, include a single metering device which, under control of a programmed controller, is capable of performing at any one time a single measurement function of a single parameter. The resultant function is displayed to a predetermined accuracy on a single, multidigit, display.
The meters of the prior art, particularly DMM's, thus include sensitive measurement circuitry as well as sophisticated control circuitry. In a DMM, for example, a programmed microprocessor may be used as the controller, together with an external keyboard or other device for inputting control signals and user commands to set a desired measurement function. Because a microprocessor controller is used, the number of measurement functions which may be performed by the meter is significantly increased. DMM's are thus expensive devices capable of sophisticated individual measurements.
A typical measurement meter utilizes a set of input leads which include probes for contacting circuit nodes at which desired parameters are to be measured. As is known in the art, typically two such input leads are required to measure an electrical parameter such as current or voltage. A DMM controller is capable of causing the measuring device to perform various functions for determining a number of characteristics of a measured electrical signal parameter, such as determining current or voltage frequency, peak or RMS AC values, DC values, impedance ratios, and the like.
In many instances it is desirable or necessary to measure several different circuit parameters, or to obtain several characteristics of one or more measured parameters, at one or more circuit points. For example, it may be necessary to determine the current or voltage at two separate circuit points, or to determine both current and voltage at a single circuit location. Alternatively, it may be necessary to measure frequency and amplitude of a signal at a particular circuit location in order to determine a frequency response of the circuit. Still further, it may be necessary to determine the impedance of one circuit parameter and to determine a voltage thereacross or a voltage or current at a different circuit location.
In each of the above illustrations, in the prior art it is necessary to use two prior art DMM's or other measurement devices for performing the necessary measurements and for providing output displays indicative of the measurement results. However, as noted above, the use of plural meters is expensive because of complete duplication of an entire measurement system. Thus, in some situations, a user may be tempted or required to use a single meter in order to reduce expenses. In such an arrangement, the user will provide a first input command to the controller (as by providing a first setting for a measurement function key) to obtain a first measurement, and thereafter will provide a second input command to the controller (as by providing a second setting for the measurement function key) to obtain the second measurement.
However, under these circumstances the measurements, which are performed by a single instrument, are separated by a significant time lapse, which is necessary for a user to enter two commands to the meter and/or to reconnect the meter input leads to different circuit points. Moreover, since only a single meter is used, the user is required to rely on his or her memory to recall both measurements.
Clearly, measurements performed in such a manner may provide erroneous results, in that values of two parameters are obtained only after substantial time separation and in that one or both of the measured parameters may be forgotten by the user or may be incorrectly recalled. In those instances where substantially simultaneous readings are necessary, and where it is necessary for a user to be provided with concurrent displays of two or more measurement results, an expensive arrangement is required in which plural meters are used.
There is thus a need in the prior art for an inexpensive device capable of performing a plurality of measurements and of providing substantially simultaneous and concurrent displays of the measurement results.